1. Field of the Invention
Apparatuses consistent with the present invention relate to a structure for connecting a flexible substrate, such as a membrane board or a flexible printed circuit board (FPC), and a terminal fitting.
2. Description of the Related Art
For a related art connection structure of this kind, as shown in FIG. I, a connection structure is configured so that: barrels 51 are formed in an upstanding manner on a lower plate of each of terminal fittings 50 which has an upper plate and a lower plate; holes 52, in which the barrels 51 in the lower plate of the terminal fittings are inserted, are formed on a portion of a circuit board 53; a reinforcing plate 54 having similar holes is disposed on the hole-formed portion of the board 53; the upper plate of the terminal fittings are lifted to insert the barrels 51 formed on the lower plate of the terminal fitting into the holes 52 formed in the circuit board 53 and the upper plate is retuned to its original position, thereby sandwiching the board 53 between the lower plate and the upper plate; the barrels 51 are bent to secure the upper plate; and the print side of the circuit board 53 and the lower plate are in contact with each other. According to this related art example, it is possible to improve workability, prevent a circuit surface from being damaged and enhance connection reliability.
For another related art example, as shown in FIG. 2, a connection structure is configured so that: each of terminals 61 is provided at one end in the longitudinal direction of a base 60; a flexible printed circuit (FPC) 62 is mounted on a mounting surface of the base 60; and the FPC 62 is pressure-bonded and secured by the outer peripheral surfaces of barrels 63 and the mounting surface, the barrels 63 extend from both sides of the base 60, and are substantially perpendicular to the longitudinal direction of the base 60, the barrels are also provided facing the mounting surface and being curved inward to form a cylindrical shape. With this configuration, the outer peripheral surfaces of the barrels 63 are in surface-contact with the FPC 62 and concentrative stress applied to the FPC 62 is thereby relaxed, making it possible to prevent the FPC 62 from being damaged. Even though the material thickness of the FPC 62 is decreased as a result of the relaxation of stress on the FPC 62 due to secular changes, an elastic force can be applied to the FPC 62 by the barrels 63, making it possible to maintain stable connection to the FPC 62 over a long period of time. These barrels 63 have a small spring constant, and accordingly, it can reduce an elastic pressure decrease caused by the decease of the material thickness of the FPC 62.
For a still another related art example, as shown in FIG. 3, a connection structure includes: a pair of metal plates 71 and 72 holding a membrane circuit 70 therebetween; two connection members 73 and 74 connecting, in a fixed manner, the pair of metal plates 71 and 72 with the membrane circuit 70 interposed therebetween; and at least one protrusion 75 formed on at least one of the pair of metal plates 71 and 72 and located in between the two connection members 73 and 74 in such a manner that it protrudes toward the membrane circuit 70.
Since the related art example shown in FIG. 1 has a structure in which protrusions are provided only to either the upper plate or the lower plate of each of the terminal fittings to make the circuit of the flexible substrate and the terminal fittings in contact with each other, it lacks connection reliability when surfaces of the terminal fittings with no protrusions and the circuit side are disposed to be contact with each other, and accordingly, it is necessary to turn the terminal fittings such that the opposite surface with protrusions and the circuit side are disposed to be in contact with each other, to fit to the circuit surface of the flexible substrate.
The related art example shown in FIG. 2 has a disadvantage in that it is difficult to maintain the balance of the contact force between the upper portion and the lower portion of the terminal fittings where a structure in which the upper portion is provided with protrusions and the lower portion is provided with holes is employed, because the contact point shape differs between the upper and lower portions. Where the balance cannot be maintained, an incorrect behavior may occur when an environmental test or the like is conducted.
The related art example shown in FIG. 3, the protrusion of the terminal fitting and the circuit surface of the flexible substrate are made in contact with each other after they are matched with each other, which results in poor workability. Also, with this related art example structure, it is difficult to employ multipolarity.